Suggest me a book (which you read in your teens) that you think had changed you into a drastically better person.

I am looking for a book (any genre, preferably fantasy) that has a deep plot and profound meaning which has to be read between the lines. The book should go over many useful life lessons, displaying both bad and good sides of life and positions all people must find themselves in at least once in their lifetime.

by SilentThespian